The Uckfield and District Preservation Society was founded in 1968 to protect and preserve the Nutley Windmill, the last operational open-trestle post mill in England.

Parts of this mill date back to around 1550, but it is believed to have been built elsewhere and brought to its current location around 1820.

The New Abbey Corn Mill, which dates back to the 18th century, also is in working order. In summer, visitors can watch demonstrations of oatmeal being made.

A third working mill, the Ballycopeland Windmill on Ards Peninsula in County Down, Northern Ireland, is featured on the top £1.40 stamp. The bottom stamp depicts the Cheddleton Flint Mill in Staffordshire, England.

A stone tower windmill, Ballycopeland was built around the turn of the 19th century and was in use until World War I. Restoration work began around 1950.

The Cheddleton Flint Mill includes two waterwheels, one of which might date back to around 1250. This mill originally was used to grind grain, but was converted to grind flint for pottery in the late 18th century.

Shown on the £1.57 stamps are Woodchurch Windmill near Ashford, Kent, England; and the Felin Cochwillan Mill at Gwynedd, Wales.

The Woodchurch Windmill is a smock mill, which means that only the cap of the windmill turns to meet the wind, as opposed to the entire post turning.

Originally, two windmills, known as “the twins,” stood together overlooking the village of Ashford, according to the mill’s website.

Build about 200 years ago, Felin Cochwillan Mill, Gwynedd, is privately owned. It originally served as a fuling (a process used in making cloth) and was later converted to grind grains, according to the website.

The firm Atelier Works designed the stamps, using photographs by Philip Sayer.

International Security Printers produced them by offset in sheets of 60 (sold in panes of 30 at most postal outlets).

The stamps measure 35 millimeters by 37mm and are perforated gauge 14.5 by 14.

The £1.40 stamps pay the rate for international letters up to 20 grams, and the £1.57 stamps meet the rate for letters to Europe up to 100 grams. The first class-rate is 65 pence.

Royal Mail’s other products for the Windmills and Watermills set include first-day covers, six postcards reproducing the designs of the stamps, and a presentation pack with mint examples of the stamps and text by Martin Watts, an expert on mills.